Such source guide systems, also called remote afterloader systems, are used with brachytherapy treatments. With such treatments, a patient is internally irradiated by means of inserted radiation sources, for the treatment of tumors. For this, one or more catheters are provided in the tissue. For this, many designs are possible, while, in addition, the position of the catheters may vary from patient to patient and the shape of the area to be irradiated may vary.
For obtaining an optimal radiation dose, various source positioning systems are used in determining the dwell positions of the source within these catheters. The length of the inserted catheter is then typically a fixed length so that always a part of the catheter needs to project outside the patient. The irradiation then takes place from the distal part of the catheter. This often has to do with the source guide system. These source guide systems often take the source out to a fixed length and then withdraw the source to the predetermined dwell positions. Other designs operate reversely; they take the source to a first position in the catheters and then step forwards to the indicated positions. The source positions and the actual position in mm need to be calculated each time. In addition, these systems typically have a maximum number of dwell positions for the source. The result of this is that, with larger irradiation areas, a plurality of these limited dwell positions results in larger step positions of for instance about 2.5 mm or about 5 mm or about 10 mm.
In order to determine these positions, often, per catheter, marker wires are provided in the catheters. On these marker wires, at every cm, markers are clamped on the wires which are then made visible by means of X-rays. Then, often a very large number of marker points arise on the X-rays which complicate determining positions and can easily be confused.
This results in a very complicated and laborious process where measuring errors regularly occur which can result in incorrect irradiations. Further, one or more catheters project far outside the patient, which can bend between irradiations or can result in movement restrictions for the patient.